1. Field of the Invention
The invention relates to the field of pacemakers and implantable electrophysiologic devices and in particular for connector heads used in pacemakers and to which the pacemaker leads connect.
2. Description of the Prior Art
Permanent implantable pacemakers are bioelectrical devices designed to monitor and maintain heart rates of patients with episodically or chronically slow or fast heart rates which produce significant symptoms. In general, the pacemakers are set to provide minimum and maximum heart rates and, through their sensing or monitoring capabilities, are designed to function on demand from sensed heart signals based upon signal analysis provided by programs stored within the pacemaker.
Pacemakers are comprised of two basic components, namely a pulse generator contained within a casing, which is subcutaneously implanted, and leads which extend from the pulse generator into the heart chamber through the veins. The pulse generator is the more complex of the two components. It is a hermetically sealed unit which is surgically implanted into a pocket created under the skin and subcutaneous fat below the clavicle on either the right or left side of the upper chest. The pulse generator contains a battery, and microprocessor that regulates the output of the pacemaker to the heart. Frequently, external communication with the pacemaker is possible by means of radio telemetry both to inquire as to the mode or the function of the pulse generator, and when necessary to reprogram that parameter. The most complex pacemakers have multiple programs with two leads disposed into two separate chambers in the heart, which programs can be selected to control the pulse generator's output.
The leads function as the electrical pathways between the pulse generator and the selected area of the heart muscle. They are most often inserted from the surgical pocket defined under the skin for the generator unit into the subclavian vein which runs to the heart. The leads are placed in a stable position within a cardiac chamber using X-ray visualization. Impulses travel in both directions over the lead to allow the pulse generator to both sense and pace the appropriate cardiac chamber or muscle tissue at the appropriate time.
The leads are generally defined as either unipolar or bipolar. A unipolar lead is a lead having one electrode, the cathode, at its distal tip. The other electrode, the anode, is comprised of the metallic casing of the hermetically sealed unit, the pulse generator. The proximal end of the unipolar lead, which connects to the pulse generator, has a single electrical contact for the cathode. Bipolar leads are defined to have both the cathode and anode at or near the distal end of the lead within the heart chamber with the cathode being the most distal. There are two electrical contacts at the proximal end of the lead connected to the pulse generator, one for the cathode and one for the anode.
Many pacemakers are now constructed or designed to be connected to bipolar leads. However, the pulse generators may be set to function either in a unipolar or bipolar mode because there are advantages and disadvantages to each. It is not uncommon to switch the mode of operation of the pacemaker from one to the other depending upon the clinical needs of the patient and the problems encountered in the function of the pacemaker in question. In addition, dedicated unipolar pacemakers connected to unipolar leads continue to be manufactured and implanted.
A specific issue with respect to the function of the unipolar pacing modes is a concern that the pulse generator might sense the electrical activity of muscles within the chest wall, such as the pectoral muscle. If this electrophysiological activity originating from the muscles is interpreted by the pacemaker as cardioactivity, the pacemaker program may shut off the output of the pulse generator. If the patient is pacemaker dependent, this in turn may cause him to lose consciousness or worse.
For this reason, only one side of the pulse generator's casing is used to function as an electrode or anode in unipolar pacing. As consequence of this fact, the hermetically sealed unit in which the pulse generator is encased must always be implanted with its anode side facing anteriorly or away from the underlying chest wall muscles. Even if the unit is implanted with the initial intention of functioning as a bipolar pacemaker, its orientation within the chest pocket must always be fixed, since it may become necessary to reprogram the unit to function in the unipolar mode at some time in the future.
Recently by agreement among pacemaker manufacturers, all pacemaker leads are designed according to a uniform specification designated as IS-1 or VS-1 to allow every company's leads to be interchangeable with every other company's pulse generator connector head. The connector head is the portion of the pulse generator to which the leads are electrically and physically connected. The leads are manufactured to a fixed length which cannot be adjusted by the surgeon in the operating room. The leads are always long enough to allow the appropriate cardiac chamber to be reached with some excess lead being provided. The excess length is then coiled into a loop around the pulse generator. The pulse generator with its coil of excess lead is then placed into the subcutaneous pocket created by the surgeon, and the skin is sutured closed.
Turn to FIG. 1 wherein a bipolar pacemaker of the prior art is depicted in plan view. Pacemaker 10 includes a connector head 12 to which a lead 14 is to be connected. Prior art pacemakers 10 have a specific physical configuration such as shown in FIG. 1. When viewed from the anode side of casing 16, which is usually the side of pacemaker 10 with the manufacturer's name or logo on it, connector head 12 at the top of pacemaker 10 is positioned such that lead 14 must be connected into connector head 12 only from the right side as seen in the configuration in FIG. 1. When lead 14 extends from the right side of connector head 12, its natural tendency is to coil in a clockwise direction around pulse generator 10. Such a configuration allows a smooth entry of the lead 14 into the subclavian vein via a surgical pocket on the right side of the chest. In some cases, it is medically advantageous to have the pacemaker on the left side of the chest either because of various aspects of the patient's anatomy or because of previous surgery involving the chest wall.
In FIG. 6 wherein a unipolar of the prior art is depicted in plan view a similar configuration to FIG. 1 occurs. Lead 82 must be connected into connector head 70 of pacemaker 10 only from the right side as seen in FIG. 6.
Returning to FIG. 1, attempts to place pacemaker 10 on the left side of the chest poses significant problems in coiling the excess length of lead 14 into the surgical pocket. A lead entering the left subclavian vein is most easily coiled around pacemaker 10 with a connector head which allows the leads to emerge from the left side of pacemaker unit 10. However, pacemaker 10 cannot be turned over to permit left side exit of lead 14 from connector head 10 because the anode side of the casing must be kept away from the underlying muscle.
Therefore, the surgeon must use pacemaker 10 in the configuration as shown in FIG. 1 even when implanted on the left side. This adds significant time in surgery and may require some enlargement or modification of the pocket. In some cases, the entire assembly of pacemaker 10 and lead 14 assumes an awkward lie or configuration within the surgical pocket with a knuckle or loop of lead 14 protruding into a corner of the pocket. Such a lead knuckle or kink may cause patient discomfort or subcutaneous protrusions which are unwanted and may lead to reoperation. The problem with the left side implantation becomes even more exacerbated in the case where the patient is to receive a pacemaker 10 having dual leads.
What is needed is a design for a connector head which will facilitate the actual surgical implantation of the entire pacemaker generator and its leads within the operating theater in either the left or right side of the patient's chest. What is needed is a pacemaker configuration which avoids each of these problems but still allows the pacemaker to be always disposed within the surgical pocket anode side up.